Core: rnotwhite -> rhtmlnotwhite and jQuery.trim -> stripAndCollapse

Core: rnotwhite -> rhtmlnotwhite and jQuery.trim -> stripAndCollapse

- Renames and changes rnotwhite to focus on HTML whitespace chars
- Change internal use of jQuery.trim to more accurate strip and collapse
- Adds tests to ensure HTML space characters are retained where valid
- Doesn't add tests where the difference is inconsequential and
  existing tests are adequate.

Fixes gh-3003
Fixes gh-3072
Close gh-3316